In transmission electron microscopy, a new specimen is cooled and then observed after the previous specimen is replaced by this new specimen or after it is treated in a vacuum. For example, where a clean surface of a specimen is observed after it is treated in a high vacuum, a device as described in Japanese Utility Model Laid-Open No. 62662/1984 has been used. This device is illustrated in FIG. 5, where the electron microscope incorporating this device includes a specimen chamber having a side wall 1. Also shown are a partition valve 2, a preliminary evacuation chamber a specimen insertion rod 4 acting also as a specimen stage, and a specimen holder 5. When the specimen holder 5 is detachably held at the front end of the specimen insertion rod 4, the holder 5 can be moved from inside the atmosphere into the specimen chamber or vice versa via the evacuation chamber 3, for replacing the holder 5 with a new one. The inside of the evacuation chamber 3 is evacuated through an evacuation tube 6. The side surface of the specimen insertion rod 4 is provided with an annular groove in which an 0 ring 7 is fitted. This 0 ring is in contact with the inner wall surface of a specimen insertion port 8 formed in the evacuation chamber 3 to maintain the airtightness.
When the specimen is observed using the device described above, the specimen holder 5 set up within the atmosphere is first attached to the front end of the specimen insertion rod 4. The front end portion of the rod 4 is inserted into the specimen chamber through the specimen insertion port 8. Then, the inside of the preliminary evacuation chamber 3 is evacuated by a vacuum pump (not shown) via the evacuation tube 6. The side wall of the chamber 3 is provided with an opening 9 to permit insertion of an attachment. A cover lo is placed over the opening 9 This cover 10 is removed, and any one of various specimen treating apparatuses is inserted into the chamber. Thus, the specimen can be treated variously while maintaining the vacuum. Then, the partition valve 2 is opened, and the specimen insertion rod 4 is inserted into the specimen chamber until its front end reaches a given position 11 indicated by the broken line. Thereafter, the electron beam is made to hit the specimen Under this condition, an electron microscope image is observed The field of view of the observed image is moved by operating a moving mechanism 12 which is attached to the rod 4 and located within the atmosphere. In order to observe the specimen after it has been cooled, it is necessary to circulate a refrigerant through a pipe (not shown) mounted inside the rod 4, for cooling the specimen holder 5. However, this pipe mounted in the insertion rod 4 supporting the specimen holder presents a problem. In particular, the refrigerant circulating through the pipe boils, producing vibration which is transmitted to the specimen This makes it difficult to observe the electron microscope image at high resolution.
Another conventional device is similar to the device described just above except that a stationary specimen stage is mounted inside the specimen chamber. Referring also to FIG. 5, the specimen holder 5 which is detachably held at the front end of the specimen insertion rod 4 is placed on the specimen stage. During the observation of the specimen, the rod 4 is placed outside the specimen chamber. The holder 5 is cooled via the stage.
With this device, no vibration is transmitted to the specimen stage. Therefore, it is relatively easy to cool the specimen holder while the specimen is being observed. However, this apparatus also suffers from a disadvantage. Specifically, after the cooled specimen is treated in a vacuum, the specimen is moved from the preliminary evacuation chamber onto the specimen stage. During this movement, the temperature of the holder shifts. In this way, it is difficult to maintain the specimen at a given temperature.